This invention relates to an integrated optical component, used in an optical pickup for recording and/or reproducing signals for an optical disc, such as a magneto-optical disc, an optical pickup device employing this integrated optical component and an optical disc device provided with the optical pickup device.
Up to now, an optical pickup for a magneto-optical disc, constructed as shown in FIG. 1, has been put to practical use.
An optical pickup 1, shown in FIG. 1, is constructed as an optical pickup for e.g., a mini-disc (MD), and includes an astigmatism correcting plate 3a, a grating 3b, a beam splitter 4, a collimator lens 5, a optical path raising mirror 6 and an objective lens 7, arranged in this order in an optical path of a light beam radiated from a semiconductor laser element 2 as a light source and proceeding towards an optical disc D, and a Wollaston prism 8a, a multi-lens 8b and a photodetector 9, arranged in this order in the optical path of the return light from the optical disc D separated by a separator film 4a of the beam splitter 4, these optical components being mounted separately from one another.
In the optical pickup 1, constructed as described above, the light beam radiated from the semiconductor laser element 2 is corrected for astigmatism by the astigmatism correcting plate 3a and subsequently split by the grating 3b into three light beams, namely a main beam and two side beams, which are respectively incident on the beam splitter 4.
A portion of the light beam incident on the beam splitter 4 is transmitted through the separator film 4a of the beam splitter and is turned into a collimated beam by the collimator lens 5. The collimated light beam then has its optical path warped by the optical path raising mirror 6 and is converged by the objective lens 7 so as to be illuminated on a signal recording surface of the optical disc D. At this time, three spots are formed on the signal recording surface of the optical disc D by the respective light beams split by the grating 3b. 
When the light beam illuminated on the signal recording surface of the optical disc D is reflected by the signal recording surface of the optical disc D, it has its polarization plane rotated, under the magnetic Kerr effect, depending on the state of magnetization (recording state) of a portion of the signal recording surface irradiated with the light beam.
The return light beam, reflected by the signal recording surface of the optical disc D, again falls on the beam splitter 4 via the objective lens 7, optical path raising mirror 6 and collimator lens 5.
Another portion of the light beam incident on the beam splitter 4 is reflected by the separator film 4a of the beam splitter 4 to fall on the Wollaston prism 8a. 
The Wollaston prism 8a is made up of two uniaxial crystals, bonded together, and separates the incident light into three light beams, namely a p-polarized light beam, an s-polarized light beam and a p+s polarized light beam (direction of polarization relative to the separator film 4a of the beam splitter 4), having respective different reflection angles, based on the difference in the orientation on the junction surface of the optical axes of the two uniaxial crystals. The return light, falling on the Wollaston prism 8a, is split into the three light beams by the Wollaston prism 8a, afforded with astigmatism and extended in optical path length by the multi-lens 8b and is received by the light receiving surface of the photodetector 9 for signal detection.
Of the return light, received by the light receiving surface of the photodetector 9, the p-polarized light and the s-polarized light, obtained on splitting by the Wollaston prism 8a, is used as basis to detect the magneto-optical signals. That is, the return light, obtained on reflection on the signal recording surface of the optical disc D with rotation of the plane of polarization and on separation by the Wollaston prism 8a into the p-polarized light and the s-polarized light, is received by the light receiving surface of the photodetector 9, whereby the state of magnetization on the signal recording surface of the optical disc D (recording state) is detected as changes in light intensity.
On the other hand, of the return light, received by the light receiving surface of the photodetector 9, the p+s polarized light, separated by the Wollaston prism 8a and afforded with the astigmatism by the multi-lens 8b, is used as basis to detect focussing error signals by the so-called astigmatic method. Also, of the return light, received by the light receiving surface of the photodetector 9, the two side beams, as split by the above-mentioned grating 3b, are used as basis to detect tracking error signals by the so-called three-spot method.
In the present optical pickup 1, the objective lens 7 is adapted to perform fine movements, based on pre-set servo signals, so that the light beam from the semiconductor laser element 2 will form a spot at a correct position on the signal recording surface of the optical disc D to reproduce correct recording signals, in order to detect correct magneto-optical signals.
That is, the so-called tracking servo of causing fine movements of the objective lens 7 along the radius of the optical disc D is effected based on the above-mentioned tracking error signals, in order for the spot of the light beam to follow the recording track of the optical disc D. On the other hand, the so-called focussing servo of causing fine movements of the objective lens 7 along the optical axis towards and away from the signal recording surface of the optical disc D is effected based on the above-mentioned focussing error signals so that the light beam will form a correct spot on the signal recording surface of the optical disc D.
Meanwhile, in the optical pickup 1, constructed as described above, the recording information written on the optical disc D is read out by plural separately mounted optical components, such that the optical pickup cannot be reduced in size or in the number of the components, thus complicating the assembling steps or the optical adjustment steps of the optical pickup to raise the production cost.
On the other hand, in the replay-only optical pickup, adapted for reading out the recording information from e.g., a compact disc (CD), an integrated optical component, obtained on integration of the semiconductor laser element as a light source and a photodetector etc, is used to reduce the size of the optical pickup and that of the optical disc device having the optical pickup built-in therein.
Meanwhile, the conventional integrated optical component, employing a non-polarization optical system as an optical system, is highly effective for use on a replay-only optical pickup. However, if the integrated optical component is to be applied to an optical pickup adapted for recording and/or reproducing a magneto-optical disc, the following problem arises.
That is, if such integrated optical component is used in an optical pickup for recording and/or reproduction of a magneto-optical disc, only the focussing error signals, not dependent on the direction of polarization, need to be detected by the light receiving element of the integrated optical component, whereas the magneto-optical signals and tracking error signals, dependent on the direction of polarization, need to be detected by a photodetector provided independently of the integrated optical component. The result is that, in this optical pickup, not only can the number of component parts not be reduced sufficiently, but detection signals are respectively detected from the two optical components, that is the integrated optical component and the photodetector, thus increasing the number of lead lines for signal lead-out and complicating the assembling operation to raise the mounting cost.
Moreover, since the polarization splitting means, such as Wollaston prisms, or cylindrical lenses for detecting the focussing error signals, as astigmatism affording means, are required for detecting the magneto-optical signals from the return light from the optical disc for the photodetector, the number of external components is increased to raise the costs for component parts and for assembling in a manner not favorable in reducing the size or improving the operational reliability.
In view of the above-described status of the art, it is an object of the present invention to provide an integrated optical component that is able to realize size reduction of the optical pickup and cost reduction and to improve the operational reliability, an optical pickup employing this integrated optical component and an optical disc device provided with this optical pickup.
An integrated optical component according to the present invention includes an integrated optical component used for an optical pickup configured for illuminating a light beam on a signal recording surface of an optical disc to record and/or reproduce signals, including a light source for radiating a light beam for illuminating a signal recording surface of the optical disc, a photodetector for receiving the return light beam reflected back from the signal recording surface of the optical disc, a package member having an opening in one major surfaces thereof and configured for accommodating the light source and the photodetector therein, an optical component provided on the major surface of the package member having the opening, the optical component being configured to transmit the light beam radiated from the light source therethrough and to transmit the return light beam proceeding towards the photodetector and light separating means provided as-one with the optical component and configured for separating the light beam radiated from the light source from the return light beam proceeding towards the photodetector. The optical component is formed as-one with focussing error signal generating means positioned on an optical path of the return light beam separated by the light separating means to proceed towards the photodetector.
In this integrated optical component, the light beam radiated from the light source is incident on and transmitted through the optical component via an opening in the package member so as to be fall on the light separating means. The return light beam separated from the light separating means then is incident on and transmitted through the optical component. At this time, the return light beam is transmitted through focussing error signal means formed as-one with the optical component. This focussing error signal generating means is used for generating focussing error signals and is comprised of, for example, a cylindrical lens or a Foucault prism.
The return light beam, transmitted through the focussing error signal generating means and through the optical component, falls on the package member via opening so as to be received by the photodetector. The playback signals and the focussing error signals etc are generated based on detection signals from the light receiving sections of the photodetector.
In this integrated optical component, the respective optical components are integrated and unified, while the focussing error signal generating means are formed as-one with the optical components, thus reducing the overall size and the number of the components.
Also, in this integrated optical component, since the light source and the photodetector are formed as a sole integral unit which is provided on, for example, a sole substrate, it is possible to reduce the number of leads used to lead out signals, to simplify the assembling operation and to reduce the assembling cost, while position registration of the light source and the photodetector may be dispensed with.
In the integrated optical components of the present invention, light splitting means for splitting the light beam into plural beams is preferably formed as one with the optical component and positioned on the optical path of a light beam radiated from the light source to proceed towards the light splitting means.
The light splitting means is comprised of a diffraction grating for splitting the light beam radiated from the light source into a main beam which is at least the zero-order light and two side beams of xc2x1 order one light. The two side beams, as split by the light splitting means, are used for generating tracking error signals.
In the present integrated optical component, in which the light splitting means is formed as-one with the optical component, the number of components can be reduced further.
In the integrated optical component according to the present invention, the light splitting means preferably includes a first separating film for separating the light beam radiated from the light source and the return light beam proceeding towards the photodetector, and a reflecting surface for reflecting the return light beam separated from the first separating film. The first optical path, as an optical path of the light beam proceeding towards the first separation film, is preferably substantially parallel to the second optical path, as an optical path of the return light beam reflected back from the reflecting surface.
With the integrated optical component, in which the first and second optical paths are substantially parallel to each other, the light source can be positioned in proximity to the photodetector, thus further reducing the overall size.
Also, with the integrated optical component according to the present invention, the first separating film of the light separating means is preferably a partial polarization separating film having differential transmittance depending on the direction of polarization of the incident light.
With the integrated optical component, in which the first separating film of the light separating means is formed as a partial polarization separating film having differential transmittance depending on the direction of polarization of the incident light, an enhancing effect for the so-called Kerr enhancement effect may be endowed. The Kerr rotation angle enhancing effect is the effect of increasing the rotational angle of the polarization plane of the return light beam incident on the light separating means.
In the integrated optical component according to the present invention, the light separating means preferably has polarization splitting means between the first separating film and the reflecting surface for polarization-splitting the return light beam from the signal recording surface of the optical disc as separated by the first separating film.
With the integrated optical component, in which the light splitting means includes polarization splitting means for polarization-splitting the return light beam. The plural return light beams, polarization-split by the polarization splitting means, are received by the photodetector for detecting the magneto-optical signals as playback signals.
Also, in the integrated optical component according to the present invention, the first separating film, the polarization splitting means and the member having the reflecting surface are preferably formed as-one with one another,
In the integrated optical component, in which the first separating film, the polarization splitting means and the member having the reflecting surface are formed as-one with one another, whereby the integrated optical component can be reduced further in size and the number of component parts can be further diminished to lower the costs incurred in component parts and in assembling further.
Also, in the integrated optical component according to the present invention, light beam adjustment means is preferably formed as one with the optical component on the optical path of the light beam radiated from the light source to proceed towards the light splitting means for converting the angle of divergence of the light beam radiated from the light source.
In the integrated optical component, provided with light beam adjustment means for converting the angle of divergence of the light beam radiated from the light source, the light beam radiated from the light source is passed through the light beam adjustment means and thereby converged to some extent, so as to be then guided to the light beam converging means of the optical pickup, whereby an objective lens of a finite multiplication factor, for example, may be used as light converging means. Thus, in the optical pickup, employing this integrated optical component, the optical component converting the light beam into a collimated light beam, such as a collimator lens, may be dispensed with to further reduce the overall size or the number of the components, thus further reducing the cost in the components or in assembling operations.
Also, with the present integrated optical component, the above-described light beam adjustment means is formed as-one with the optical component, whereby it is possible to reduce the size further and the number of component parts to further reduce the costs incurred in component parts and in assembling.
Also, in the integrated optical component, the above-described objective lens adjustment means preferably has differential conversion factors for the tangential and radial directions.
In the integrated optical component, in which the objective lens adjustment means preferably has differential conversion factors for the tangential and radial directions, it is possible for the light beam adjustment means to have the function of correcting the astigmatism of the light beam which is radiated from the light source so as to be illuminated on the optical disc. Thus, in the present integrated optical component, there is no necessity of providing separate astigmatism correcting plate, thus realizing further size reduction and reduction in the number of components to reduce the costs incurred in components and in assembling operations.
An optical pickup for illuminating a light beam towards a signal recording surface of an optical disc for recording and/or reproducing signals, according to the present invention, includes an integrated optical component, and light converging means for converging the light beam for illuminating the converged light beam on the signal recording surface of the optical disc. The integrated optical component includes a light source for radiating a light beam for illuminating a signal recording surface of the optical disc, a photodetector for receiving the return light beam reflected back from the signal recording surface of the optical disc, a package member having an opening in one major surfaces thereof and configured for accommodating the light source and the photodetector therein, an optical component provided on the major surface of the package member having the opening, and light separating means provided as-one with the optical component and which is configured for separating the light beam radiated from the light source from the return light beam proceeding towards the photodetector. The optical component is configured to transmit the light beam radiated from the light source therethrough and to transmit the return light beam proceeding towards the photodetector therethrough. The optical component is formed as-one with focussing error signal generating means positioned on an optical path of the return light beam separated by the light separating means to proceed towards the photodetector.
In this optical pickup, the light beam radiated from the light source of the integrated optical component falls on the optical component via the opening in the package member so as to be transmitted through the optical component to fall on the light splitting means. The light beam transmitted through the light separating means then is radiated from the integrated optical component.
The light beam, thus radiated from the signal recording surface of the optical disc, is converged by the light converging means so as to be illuminated on the signal recording surface of the optical disc.
The return light beam radiated from the signal recording surface of the optical disc is re-transmitted through the light beam converging means to fall on the light splitting means of the integrated optical component. The return light beam incident on the light separating means is thereby separated from the return light beam proceeding towards the optical disc. The return light beam, separated by the light separating means, is incident on and transmitting through the optical component. At this time, the return light beam traverses focussing error signal means formed as-one with the optical component. This focussing error signal means is used for generating focussing error signals and is made up of, for example, a cylindrical lens or a Foucault prism.
The return light beam, traversing the focussing error signal means and transmitting through the optical component, falls on the package member via the opening so as to be received by the photodetector. Based on the detection signals from the light receiving sections of the photodetector, the playback signals or the focussing error signals etc are generated.
In the present optical pickup, the integrated optical component is constructed by integrating and unifying the focussing error signal generating means with the optical component, the overall size and also the number of components may be reduced.
Also, in the present optical pickup, the light source and the photodetector of the integrated optical component are constructed as a sole integral unit, mounted on e.g., a sole substrate, it is possible to reduce the number of leads for signal lead-out and the assembling cost as well as to simplify the assembling operations. Moreover, the position registration between the light source and the photodetector may be dispensed with.
In the optical pickup according to the present invention, there is preferably provided between the integrated optical component and the light converging means a reflecting member for reflecting the light beam from the integrated optical component to cause the reflected light beam to proceed towards the light converging means, the reflecting member reflecting the return light transmitted through the light converging means to cause the reflected light to proceed towards the integrated optical component.
In the optical pickup, constructed as described above, the optical path from the integrated optical component to the reflecting member can be substantially collimated with respect to the signal recording surface of the optical disc, thus enabling the thickness to be reduced.
An optical disc device according to the present invention includes an optical pickup for illuminating a light beam on a signal recording surface of an optical disc to detect the return light from a signal recording surface of the optical disc, a biaxial actuator for supporting the light converging means provided on the optical pickup for movement in bi-axial directions, a signal processing circuit for generating playback signals based on a detection signal from a photodetector provided on the optical pickup and servo means for causing movement in the bi-axial directions of the light converging means provided in the optical pickup based on a detection signal from the photodetector provided on the optical pickup. The optical pickup includes a light source for radiating a light beam for illuminating a signal recording surface of the optical disc, a photodetector for receiving the return light beam reflected back from the signal recording surface of the optical disc, a package member having an opening in one major surfaces thereof and configured for accommodating the light source and the photodetector therein, an optical component provided on the major surface of the package member having the opening, the optical component being configured to transmit the light beam radiated from the light source therethrough and to transmit the return light beam proceeding towards the photodetector and light separating means provided as-one with the optical component and configured for separating the light beam radiated from the light source from the return light beam proceeding towards the photodetector. The optical component is formed as-one with focussing error signal generating means positioned on an optical path of the return light beam which is separated by the light separating means to proceed towards the photodetector.
In the present optical disc device, the light beam radiated from the light source of the integrated optical component is incident via the opening in the package member and transmitting through the optical component so as to be again incident on the light separating means. The light beam transmitted through the light separating means is radiated from the integrated optical component.
The light beam radiated from the integrated optical component is converged by the light converging means so as to be illuminated on the signal recording surface of the optical disc.
The return light beam, reflected from the signal recording surface of the optical disc, again traverses the light traversing means to fall on the light separating means of the integrated optical component. The return light beam, incident on the light separating means, is separated by the light separating means from the light beam proceeding towards the optical disc. The return light beam, thus separated by the light separating means, is incident on and transmitted through the optical component. At this time, the return light beam traverses the focussing error signal means formed as-one with the optical component. The focussing error signal means is adapted to generate the focussing error signals and is made up of, for example, a cylindrical lens or a Foucault prism.
The return light beam, traversing the focussing error signal means and transmitted through the optical component, is incident via the opening on the package member so as to be received by the photodetector.
In the present optical disc device, playback signals are generated in the signal processing circuit based on detection signals from the photodetector in the integrated optical component.
In the present optical disc device, focussing error signals and the tracking error signals are generated, based on a detection signal from the photodetector of the integrated optical component. Based on these focussing error signals and the tracking error signals, a biaxial actuator is driven by the servo means, so that the light converging means provided on the optical pickup is driven in a biaxial direction, that is in a direction along the radius of the optical disc or in a direction approaching to or receding away from the signal recording surface of the optical disc, by way of performing focussing servo and tracking servo operations.
In the present optical disc device, in which the respective optical components of the integrated optical component are integrated and unified to a sole unit, and in which the focussing error signal generating means are provided as-one with the optical component, the optical pickup and the optical disc device can be reduced in size, whilst the number of component parts may also be diminished.
Also, in the present optical disc device, in which the light source and the photodetector of the integrated optical component are integrated and unified to a sole unit, which is provided on e.g., a sole substrate, it is possible to reduce the number of leads for signal lead-out and the assembling cost as well as to simplify the assembling operations. Moreover, the position registration between the light source and the photodetector may be dispensed with.